Assessment Comments
Assessment is based on results of (1) ISU lake survey in 2000-04, (2) ISU reports on lake plankton communities, 2000-05, and (3) surveys by IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "fully supporting " The Class B(LW) aquatic life uses remain assessed (evaluated) as "partially supporting" due to siltation and water quality impacts of common carp. Fish consumption uses remain “not assessed.” The sources of data for this assessment include (1) results of the statewide survey of Iowa lakes sponsored by IDNR and conducted from 2000 through 2004 by Iowa State University (ISU), (2) information from the IDNR Fisheries Bureau, and (3) information on plankton communities collected at Iowa lakes from 2000 through 2005 as part of the ISU lake survey.
EXPLANATION: Results from the ISU statewide survey of Iowa lakes suggest “full support” of the Class A uses of Badger Lake. Using the median values from this survey from 2000 through 2004 (approximately 15 samples), Carlson’s (1977) trophic state indices for total phosphorus, chlorophyll-a, and Secchi depth are 69, 51, and 60, respectively. According to Carlson (1977), the index value for total phosphorus places this lake at the lower range of hyper-eutrophic lakes; the index value for chlorophyll-a, however, is much lower and is at the boundary between mesotrophic and eutrophic lakes. The index value for Secchi depth is in the lower range between eutrophic and hyper-eutrophic lakes. These index values suggest (1) high levels of phosphorus in the water column, (2) very low, and much less than expected, production of suspended algae, and (3) relatively good, and better than expected, water transparency. According to Carlson (1991), the occurrence of a high TSI value for total phosphorus with relatively low values for chlorophyll-a and secchi depth indicate that some factor (e.g., nitrogen limitation, zooplankton grazing, or some other factor) limits production of algae. The ISU lake data suggest that algal production at Badger Lake is limited by zooplankton grazing and possibly by inorganic turbidity. Based on median values from ISU sampling from 2000 through 2004, the ratio of total nitrogen to total phosphorus for Badger Lake is 162, thus indicating excess nitrogen in the water column (note: Badger Lake had the highest median summer total nitrogen over the 2000-04 period (14.7 mg/l) of any of the 131 lakes sampled for the ISU survey). The levels of inorganic suspended solids at this lake are moderately high and do suggest the potential for reducing water transparency due to high turbidities. The median level of inorganic suspended solids in the 131 lakes sampled for the ISU lake survey from 2000 through 2004 was 5.2 mg/l; the median level at Badger Lake was 6.0 mg/l.
The suppression of algal production through zooplankton grazing, however, appears possible. In terms of all Iowa lakes sampled, data from the ISU survey show relatively large populations of zooplankton species at Badger Lake that graze on algae. Sampling from 2000 through 2005 showed that Cladoceran taxa (e.g., Daphnia) comprised approximately 45% of the dry mass of the zooplankton community of this lake. The average per summer sample mass of Cladoceran taxa over the 2000-2005 period (125 mg/l) was the 41st highest of the 131 lakes sampled.
The presence of nuisance aquatic species (i.e., bluegreen algae) does not appear to be a significant problem at this lake. Data from the ISU survey suggest that bluegreen algae (Cyanophyta) comprise a relatively small portion (approximately 20% wet mass) of the summertime phytoplankton community of this lake. The median summer sample mass of bluegreen algae during the 2000-2004 period at this lake (0.08 mg/l) was the second lowest of the 131 lakes sampled. Thus, although blooms of bluegreen algae do sometimes occur, the presence of bluegreen algae at this lake does not appear to either threaten or impair designated uses.
The eutrophic conditions at this lake, along with information from the IDNR Fisheries Bureau, suggest that the Class B(LW) aquatic life uses should remain assessed as "partially supported." Water quality conditions at this lake are stable but not improving. The lake continues to receive some silt from the watershed. Common carp are a major problem in keeping the water turbid in the upper arm of the lake. Fish growth, especially crappie, however, has greatly improved. The ISU lake survey data show good chemical water quality at this lake. These data show no violations of the Class B(LW) criteria for dissolved oxygen in the 13 samples collected, or for pH in the 15 samples collected, at Badger Lake during summers of 2000 through 2004.
The fish consumption use remain "not assessed" due to lack of fish tissue monitoring at this lake.
